It is clinically important to measure a specific component in blood, for example, antigens, antibodies, proteins, or endocrines. A serum or plasma is commonly used as a blood sample and, in this case, a serum or plasma is generally separated from whole blood as rapidly as possible to avoid hemolysis. This is because, when blood cells are contained in a sample or hemolysis occurs, for example, in an immunoassay, there is a possibility of the occurrence of the effects of hemolysis on an optical system, an inhibition of an immunoreaction by internal components of blood cells, an aggregation of insoluble carriers used as a solid phase caused by a membrane component of blood cells, or an interference by adsorption or the like. Therefore, it is a conventional procedure in general clinical laboratory tests to remove blood cells from collected whole blood by centrifugation and to use the resulting serum or plasma as a sample to be tested.
However, since a dedicated device such as a centrifuge is necessary for the removal of blood cells, and the procedure needs time and effort, it is preferable to use whole blood as a sample without pretreatment, for a general practitioner not having such a device or in an unrespited emergency test, and various methods have been proposed.
For example, Japanese Unexamined Patent Publication (Kokai) No. 10-48214 (patent reference 1) discloses a method for using completely hemolyzed whole blood by sonicating whole blood or mixing whole blood with a hypotonic solution. Japanese Unexamined Patent Publication (Kokai) No. 6-265554 (patent reference 2) discloses a method of analyzing a biochemical component of blood, comprising the steps of determining whether or not a sample contains blood cells; when the result that the sample contains blood cells is obtained, determining whether or not only one or more measurable items which can be analyzed by using a sample containing blood cells are selected; and when the result that only measurable item(s) which can be analyzed by using a sample containing blood cells are selected is obtained, stirring the sample and measuring the stirred sample.
However, the method for completely hemolyzing whole blood disclosed in the above patent reference 1 has several problems, for example, various states of hemolysis. Further, interferences which flow from the inside of blood cells to a reaction system, such as hemoglobin or substances derived from the cell nucleus, sometimes seriously affect the measurement by causing a nonspecific reaction or, particularly in an immunological assay, an interfering of immunoreaction.
With respect to the method of analyzing a biochemical component of blood disclosed in the above patent reference 2, a method of determining the kind of the sample (i.e., whether or not the sample contains blood cells) is not fully disclosed. The patent reference 2 only discloses that a means for determining the kind of a sample, such as a transmission optical sensor, may be located over cuvettes encapsulating a reagent, a sample, a diluent, or the like. Further, a concrete procedure and criterion for the determination are not disclosed in the patent reference 2, except for the disclosure that, when a sample contains blood cells, a hematocrit compensation should be carried out by stirring the sample.    [patent reference 1] Japanese Unexamined Patent Publication (Kokai) No. 10-48214    [patent reference 2] Japanese Unexamined Patent Publication (Kokai) No. 6-265554